A major obstacle to the more efficient operation of internal combustion engines, and of many other contrivances that employ fluid valves, is the power required to open and close such valves at high speed. This power often exceeds the power that can be developed by a practical solenoid actuator and through hydraulic actuators controlled by servo-valves are capable of supplying the necessary speed and force, these latter are both expensive and excessively inefficient. For nearly a century the intake and exhaust valves of internal combustion engines have therefore employed a camshaft and heavy valve springs to provide the high force required to open and to close, respectively, intake and exhaust valves. This rigid, inflexible and "brute force " method of valve actuation is devoid of all possibility of adapting the timing of valve opening and closing to the variable speed and load of the engine, with the consequence that engine torque and efficiency are sacrificed at both low and high speeds. The choice of the cam profile for the camshaft of an internal combustion engine is a compromise which has no truly satisfactory solution.
In a previous patent application, "Programmed Valve System for Internal Combustion Engines," Ser. No. 306,399, filed Nov. 14, 1972, as a continuation-in-part of a prior patent application, Ser. No. 125,520, filed Mar. 14, 1971, both assigned to the assignee of the present application, two classes of engine valve actuators were described, both hydraulically powered; one in which the valve actuators were controlled by engine-driven hydraulic control valves whose timing was susceptible to computer control, and a second class in which the engine valve actuators were controlled by a single-stage solenoid hydraulic valve. In that prior patent application, means were also shown for operating the solenoid at high speed and high efficiency, using inductors as energy storage and recovery means. In a subsequent patent application, "High Speed Electromagnet Control Circuit," Ser. No. 377,956, filed July 10, 1973, as a continuation-in-part of a prior patent application, Ser. No. 308,268, filed Nov. 21, 1972, an improved circuit was described for the high speed, high efficiency control of electromagnets by means of switching circuits only.
Both of the copending aforementioned U.S. patent applications, Ser. Nos. 306,399, filed Nov. 14, 1972, and 377,956, filed July 10, 1973, are incorporated herein by reference.